Panel lamp seal



March 15, 1966 R. s. CHRISTY 3,

PANEL LAMP SEAL Filed May 1, 1961 4 Sheets-Sheet 1 lm/en tor'. Richard S. Chris tg His Ai rrovneg March 15, 1966 R. s. CHRlS-TY PANEL LAMP smu- 4 Sheets-Sheet 2 Filed May 1, 1961 lnvesn tov 4 Richafd S. ChT'iStS Hus A t tovneg March 15, 1966 R. s. CHRISTY PANEL LAMP SEAL 4 Sheets-Sheet 5 Filed May 1, 1961 9 1.5 m W r a 0 n 5 T ed La vv A Im m March 15, 1966 R. s. CHRISTY 3,240,861

PANEL LAMP SEAL Filed May 1, 1961 4 Sheets-Sheet L Inven tov: Richard 5. Chris-t5 b5 5 His AtFtOTTWSH United States Patent 3,240,861 PANEL LAMP SEAL Richard S. Christy, Willoughby, Ohio, assignor to General Electric Company, a corporation of New York Filed May 1, 1961, Ser. No. 106,829 3 Claims. (Cl. 17417.05)

This invention relates generally to the manufacture of sealed vitreous devices and lamps, and specifically to fluorescent panel lamp structures and their manufacture.

In fluorescent panel lamps, the discharge path is a tortuous or labyrinthine channel formed between two vitreous components sealed together along their margins. Such lamps provide a relatively long discharge in a small area; this is an advantage from the point of view of compactness of source and ease of handling. They offer what may be described as an area light source as against a line source as is the case with the usual elongated fluorescent lamp. These advantages of fluorescent panel lamps are rather obvious and this probably explains why such lamps have so often been proposed over the years. However no practical fluorescent panel lamps have ever resulted from such prior proposals nor have any found their way to the market place.

The bare concept of a fluorescent panel lamp is deceptively simple. One may take by way of example the square six-channel panel lamp described herein. It comprises two glass components, a backplate and a faceplate sealed together along their margins. The backplate has six parallel grooved sections or channelways extending side by side and joined together at alternate ends to provide a continuous grid-like channel. The envelope is coated internally with a phosphor, electrodes are sealed into the ends of the channel, the lamp is exhausted and a mercury vapor and inert gas filling provided, and a fluorescent panel lamp is expected to result. This is about as far as the prior art has proceeded. It has hardly explored the problem and is quite unaware of the many pitfalls that exit.

It has been suggested that a panel lamp be made by taking two sheets of glass of the desired size heated to plasticity, overlying one by the other, sealing the edges together by additional heat, and then forming the desired channelways by placing the sealed plates in a suitable mold and blowing air between them, assisted by vacuum on the outside if desired. This may result in an envelope of the desired configuration, but does not lead to practicable lamp manufacture. In the first place one would have to coat such an envelope internally with a phosphor; this means introducing a liquid suspension into the channelways, flushing it around, then draining out the excess and drying the coating. This cannot be done practically except by having holes in the ends of the channelways for draining the excess suspension and circulating drying air. Secondly, the phosphor coating must be lehred, that is the organic binder driven out by heat. A complex glass structure such as a panel lamp can only be heated very slowly, a matter of a few degrees per minute; otherwise the strains introduced by uneven temperature gradients will crack the envelope. Therefore several hours must be taken to slowly heat the lamp to lehring temperature; this is quite impractical for mass production of electric lamps. Even if the lehring problem should be overcome, the holes required at the ends of the channelways to drain out the coating suspension would then have to be plugged up, and this again is quite impractical.

The sealing of electrodes into such an envelope might be done using a conventional electrode stem or mount of the kind used with elongated tubular fluorescent lamps. This of course presents no great difliculty on a laboratory scale. However it presents great difficulties for volume 3,240,861 Patented Mar. 15, 1966 ice production. Even after the electrodes have been sealed in, there remains to be done the activation of the electrodes, the flushing out of the deleterious gases and contaminants resulting from electrode activation, the introduction of the mercury and inert gas filling and finally the complete sealing-off of the envelope which is generally referred to as tipping-off. All of these operations present special problems or difficulties on account of the unusual shape of the fluorescent panel lamp.

The principal objects of the invention are twofold and complementary to each other. The first is to provide a fluorescent panel lamp structure which is amenable to mass manufacturing processes and techniques. The second is to provide manufacturing processes or apparatus which can be used to make the panel lamp structure in question. In this regard there has been mutual interaction between lamp structure and manufacturing processes. The desired attributes of structure have in part determined the processes which must be followed and at the same time the limitations in the processes have influenced the choice of structure.

Other but nonetheless important objects of the invention are to provide novel vitreous structures, a novel panel lamp sealing process, a novel process for sealing in the electrodes, a novel process for exhausting lamps in general and this lamp in particular, a novel process for tipping-off lamps, and novel apparatus for effecting the processes.

The preferred fluorescent panel lamp of the invention utilizes vitreous plates which are preformed, phosphor coated, and lehred prior to sealing together. This eliminates the difficulties mentioned above in connection with phosphor coating, heating and lehring a pre-sealed vitreous structure.

The usual methods of working and sealing vitreous structure do not lend themselves well to the sealing of relatively large plates or panels of glass to each other. Unless the two plates are closely matched to each other, such as by grinding the mating surfaces of the plates and by trimming their edges to substantially identical dimensions, bot-h flame sealing and electrical resistance sealing are very diflicult at the rates necessary for volume production. The necessity for observing very close tolerances in the component glass plates make these methods inordinately expensive and therefore unsuitable. Furthermore, both flame and electrical resistance sealing rely on heating the glasses to be sealed together to a sufficiently high temperature that they will flow together substantially of their own accord. In the case of ordinarily lime glasses, this temperature is of the order of 800 to 900 C. However such high temperatures soften the glass and immediately this introduces the problem of warpage of the plates and deformation of the grooved channel-ways in the backplate and any configuration in the faceplate.

In accordance with a feature of the invention, I seal the vitreous plates together at relatively low temperatures while the glass is still relatively hard and cannot, in the ordinary meaning of the term, he considered soft. Along with relatively low sealing temperature, I provide very high sealing pressures, well in excess of pounds per square inch and preferably in excess of 1000 pounds per square inch. For instance in the. case'of lime glass plates, I provide sealing temperatures in the range of 600 to 650 C. and apply pressures over the areas of the glass where sealing is to be effected, of approximately 3000 pounds per square inch. An advantage of my sealing method is that it makes unnecessary the use of elaborate burner assemblies or electrical sealing power supplies with their associated maintenance problems and hazards. Also the contamination which high temperature gas sealing might introduce into the lam envelope is avoided.

A feature of the ledge or margin seal produced by my low temperature high pressure sealing method is that it is achieved with a rounded fillet at the juncture of the two glass plates. It is essential in sealing glass parts together to avoid the formation. of a sharp crack at the juncture. In other words the glass surfaces cannot come together tangentially but must do so with a reverse curve or fillet at the juncture. Otherwise the concentration of stress at the juncture will result in a weak unsatisfactory joint. I had feared that my low temperature high pressure sealing method might be defective on that score. Fortunately, it has been entirely successful and arounded fillet is produced at the juncture so that a strong seal results.

Another feature of my sealing method is that it makes it possible to seal electrode inleads directly through the sealed rim or ledge ofthe lamp at the same time as the glass plates are sealed together. The need for subsequently sealing-in conventional lamp mounts or stems is thus avoided. Since the rim of the lamp is sealed at a relatively low temperature and there is no need to play hot flames along the edge as with flame sealing, there is no danger of burning the inleads or contaminating the electrodes at sealing.

According to another feature of my invention, I exhaust, gas fill, and tip-off the lamp without using any exhaust tube intheconventional sense of the word. The conventional glass exhaust tubes with small inside diameters: and long lengths lengthen the evacuation time of a lamp considerably. In the case of a panel lamp, they create special dilficulties. Long lengths of exhaust tubing are needed to reach the outside of the oven for coupling to the exhaust system. Such long exhaust tubes of glass are prone to sagging and other distortion which makes coupling by the usual compression rubbers very difiicult. Furthermore, such exhaust tubes, at least two of them for each lamp, would have to be sealed to the lamp envelope and this also presents difficulties. Excessive build-up of glass at the point of sealing hinders the annealing process of the lamp later on, and also is objectionable in appearance on the finished lamp.

In accordance with my exhausting process, I utilize large diameter metal exhaust tubes as part of an exhausting apparatus and these are coupled directly to exhaust passageways or ports formed in the ledge seal of the lamp. The forward tip or nose of each exhaust tube is tapered and engages directly the rim of the exhaust port. The tips of the exhaust tubes are heated substantially to the temperature of the glass and the glass itself at the openings is raised above the strain point but not to such a high temperature as to soften it. The exhaust tubes are pressed sufii'ciently hard against the exhaust apertures or ports in the ledge seal of the lamp to cause some plastic fiow of the glass at the juncture; I have found that this procedure achieves a hermetic joint.

According to another feature of my invention, the exhaust passageways in the ledge seal of the lamp envelope, the rims of which are engaged by the metal exhaust tubes, are collapsed in order to seal-off or tip-off the envelope. This is done at the completion of the various flushing, activating, and gas-filling steps of the exhaust schedule. It may be accomplished by playing small sharp fires over the opening or passageway in order to collapse the glass and seal the passageway. This process may be assisted through the use of a heated blade or wedge which is pressed down over the opening and forms a blade-notch in the ledge seal transverse to the passageway, effectively sealingit off.

For further objects, features and advantages and for a more complete description of my invention, attention is now directed to the following detailed description of an i embodiment illustrating a preferred lamp structure and a preferred manufacturing process used to make it. The detailed description is to be read in conjunction with the accompanying drawings. The features of the invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawings:

FIG. 1 is a plan view of a fluorescent panel lamp embodying my invention, showing the faceplate part cut away to reveal the backplate.

FIG. 2 is a plan view through a sectioned oven and showing associated apparatus in partly diagrammatic form by means of which the lamp manufacturing process of my invention may be carried out.

FIG. 3 is a pictorial view of a lamp carrier or dolly used in conjunction with the oven of FIG. 2.

FIG. 4 is a side view, partly sectioned, through the press located in the oven and used to seal the lamp rim, the two plates of the lamp being shown on a transport dolly and opened up for electrode insertion.

FIG. 5 is a view similar to FIG. 4 showing the lamp lifted up into the mold by the die on the press platens.

FIG. 6 is a transverse sectional view through the press and lamp and showing the center press first engaging the lamp.

FIG. 7a is a side, part-sectional view through the press and oven wall and showing the metal exhaust tube engaging the rim of the exhaust passageway in the ledge seal of the lamp. FIG. 7b is a fragmentary repeating View showing the tipping-off fire playing on the glass above the exhaust passageway. FIG. 7c is a fragmentary repeating view showing the tipping-off blade moved down to seal off the exhaust passageway.

FIG. 8 is a side elevation view to illustrate the transfer of the sealed lamp from the grid die on the press platen to the transport dolly.

FIGS. 9a and 9b are fragmentary transverse cross-sectional views through the lamp, the former prior to sealing and the latter after formation of the ledge seal, and illustrating the curved fillet at the juncture.

FIGS. 10a and 10b are fragmentary side sectional views showing the nose of the metal exhaust tube engaging the rim of the exhaust passageway in the ledge seal of the lamp. The former view shows the tipping-01f fire playing on the glass above the exhaust passageway and the latter view shows the tipping-off blade moved down to completely seal off the passageway.

FIG. 11 is a pictorial view of the electrode bridge structure used herein in lieu of a conventional mount.

FIG. 12 is a fragmentary end view of the sealed and tipped-off lamp illustrating particularly the inlead seals and the tipped-01f exhaust passageway.

FIG. 13 is a plan view corresponding to FIG. 12.

General lamp structure Referring to the drawings and more particularly to FIGS. 1, 6 and 8, the illustrated six-channel lamp 1 is in the form of a generally flat square panel made up of a pair of complementary molded glass components or plates 2, 3. Component 2 forms the underside or faceplate of the lamp which is exposed to view when the lamp is mounted in its fixture or incorporated into a ceiling. It is provided with a plurality of shallow embossments 4 which may be of square outline in plan view, giving it somewhat the appearance of a quilt or checkerboard. The quilting of the faceplate improves the appearance and increases the strength of the assembly, as more fully described and claimed in my copending application Serial No. 69,314, filed November 15, 1960, entitled Quilted Faceplate for Panel Type Fluorescent Lamps, and assigned to the same assignee as the present invention. The backplate 3 is molded or blown to define, in cooperation with the faceplate, a winding or labyrinthine discharge channel or passage by means of six parallel grooved sections or channelways 5 extending side by side. The channelways are joined together at opposite ends, as at 6 Where the lengthwise partitions 7 end, thereby forming a continuous grid-like channel. Both plates may be formed from fiat sheets of glass by any suitable means, for instance by vacuum molding.

The flat rims or margins of the faceplate and backplate are hermetically sealed together to form a fused margin or ledge seal 9 running around the four sides of the lamp. According to a feature of my invention to be more fully described below, the sealing of the margins is done directly by fusion of the glass at relatively low temperatures and at very high pressures. Along the internal junctures 6 where the glass components abut together to make partitions defining the various channelways which form the labyrinthine discharge channel, the vitreous plates are not sealed together but merely pressed together into close conformity. Provided there is close tight fit or conformance of the glass plates along the junctures, the electric discharge or are will not leak through and short circuit at these partitions but will follow the labyrinthine channel through from end to end.

The lamp is provided with discharge supporting electrodes 10 at opposite ends of the channel. Each electrode (best seen in FIG. 11) comprises a coiled coil filament 11 of tungsten wire coated with alkaline earth electron-emitting oxides (carbonates prior to activation). The filament is supported across the hooked ends of inleads 12, 13 each of which comprises a nickel inner section a, a dumet (Copper-sheathed iron) section b and a copper outer section c. The three sections of each lead are welded together and the intermediate dumet section including the weld junction is the part which is sealed through the glass of the marginal ledge 9 where the faceplate and backplate are fused together. To facilitate sealing, the intermediate dumet section may be previously sheathed with a glass sleeve 14 fused thereto. The assembly shown in FIG. 11 may be termed a filament bridge and is used in lieu of a conventional filament mount in the sealing process according to my invention. The glass bead bridge 15 is a spacer and stiffener to prevent strain on the filament, particularly during handling prior to sealing into the vitreous lamp assembly. The margin of the backplate is notched inwardly from the outer edge at 16 and 17 (see FIGS. 12, 13 in order to permit the outwardly projecting ends of the inleads to be turned up for connection to the base terminals. This avoids taking the inleads all the way to the outer edge of the marginal ledge where they might present a shock hazard and is a feature described and claimed in copending application Serial No. 106,828, filed of even date herewith, of Edward V. Parillo and William C. Martyny, entitled Panel Lamp Inlead Structure, and assigned to the same assignee as the present invention. The electrodes are preferably of the low thermal capacity rapid start type which are heated at starting and during operation by passing current therethrough, but other types of electrodes may of course be used.

The lamp contains an ionizable atmosphere including a starting gas or mixture of one or more of the inert rare gases of Group 0 of the Periodic Table at a low pressure, for instance argon at a pressure of 0.5 to 5, preferably 2 to 3 millimeters of mercury, along with mercury vapor. The quantity of mercury added exceeds that vaporized during normal operation of the lamp wherein it exerts a partial pressure in the range of 2 to 10 microns, more commonly 5 to 8 microns for optimum generation of 2537 A. This radiation energizes a phosphor coating applied to the inside surfaces of the faceplate at 18 and of the backplate at 19 (best seen in FIGS. 9 and 10) the phosphor in turn producing visible light. Desirably the phosphor covers the entire faceplate and there is phosphor disposed between the vitreous walls at the channelway partitions 7 (see FIG. 9b). This is highly desirable in order to obtain a uniformly white faceplate of attractive appearance whether the lamp is lit or unlit, and is a feature described and claimed in copending application Serial No. 106,822, filed of even date herewith, of William C. Martyny, entitled Fluorescent Panel Lamp and Coating Process Therefor, and assigned to the same assignee as the present invention. The phosphor may be applied more sparingly on the faceplate, or alternatively a reflecting coating may be applied to the backplate, to cause the lamp to emit a greater proportion of its light downwardly through the faceplate than through the backplate.

The lamp may be provided with base terminal structures which may be seated on the marginal ledge seal 9, one in proximity to each electrode. Such bases may be attached to the marginal ledge by means of clips which engage furrowed notches 20 formed in the faceplate side of the marginal ledge (best seen in FIGS. 12 and 13). The notches 20 may be formed at the same time as the faceplate and backplate are being sealed together by providing a reciprocal configuration in the die of the press at the appropriate places. The base terminal structures are more fully described and claimed in copending application Serial No. 106,827, filed of even date herewith, of Albert F. Pate, Robert A. Kuebler and Harold R. Kestner, entitled Panel Lamp Base, and assigned to the same assignee as the present invention.

Manufacture The equipment which I have used in manufacturing fluorescent panel lamps is in general laboratory or pilot shop type equipment. The choice of particular mechanical apparatus was often made on the basis of immediate convenience and versatility and is not intended to be indicative of best engineering practice for volume production. This equipment has successfully been used to manufacture a substantial quantity of fluorescent panel lamps of the configuration illustrated in FIG. 1. These are square panel lamps, approviately 12" to a side, and are operable at 70 watts with a lumen output in excess of 5000 lumens. The equipment is therefore illustrative of the principles and method of the invention and of apparatus suitable for carrying them into effect. The various parts have been drawn approximately to scale, even though in places somewhat diagrammatic in style, wherever the lamp appears in relation to them, and a general idea of the size of the equipment required may be gathered therefrom.

The lamp manufacture is conducted in a furnace indicated generally at 21 in FIG. 2. It has fire brick walls which are lined internally with electric resistance heating elements (not shown in the drawing). It has an entrance opening at 22 and a lateral exit opening at 23 which are normally closed by vertically moving insulated doors diagrammatically indicated at 24 and 25 respectively. An internal fire brick partition 26 reaching partly across the oven divides it into two zones, a lehring zone to the left of the partition and a sealing zone to the right thereof. The oven wall directly opposite the entrance door is provided with two relatively small apertures 27 through which a pair of mount heads indicated generally at 28 and a pair of exhaust-tipping heads indicated generally at 29 may penetrate into the sealing zone of the oven and engage the lamp.

The lamp is transported Within the oven by means of carriers or dollys 31, 32 and 33, which for convenience will be designated respectively front, rear and side dollies. The rear dolly 32 is indicated pictorially in FIG. 3 and is generally representative of all three. It comprises a carrier in the form of a double-timed fork 34 supported atop a standard 35 which rides on a pair of rigid horizontal guide rods 36. The dolly is caused to translate by means of a rack and pinion 37, 38, the pinion being driven by an electric motor 39 fast to the standard. The guide rods, rack, pinion, electric motor and controls therefor including limit switches are of course located below the bottom wall of the oven indicated at 40. Only the fork and the upper part of the standard project into the oven proper. The front and rear dollies project through lengthwise slot 41 and the side dolly projects through lateral slot 42 in the oven floor. The front and side dollies are at approximately the same level or vertical height relative to the oven floor. The fork of the rear dolly is at a higher level and can ride over those of the other two without interference.

Loading and lelzring The lamp components, that is the faceplate 2 lowermost and the backplate 3 uppermost are loaded into a grid 43 which is in the form of a square frame provided with lengthwise running bars 44 which conform to the faceplate design. The grid 43 is eventually used as a die in the sealing operation and the arrangement of the bars is clearly seen in FIG. 6, being such as to underlie the partition junction '7 in the backplate. The grid engages the tines of the front dolly 31 by means of ears 4-5 which are lateral extensions of the transverse bars. The backplate and faceplate have previously been phosphor-coated, preferably per the process of the William C. Martyny application entitled Fluorescent Panel Lamp and Coating Process Therefor. Briefly, the entire faceplate is phosphor-coated except for the margin, and likewise the entire backplate except for the margin and the edges or flats of the partitions 7. It is desirable to back the front dolly and the grid out of the oven just prior to loading in order to have it substantially at the oven temperature and also to preheat the lamp plates in order to reduce heat shock.

Front dolly 31 is provided with a hinged latch 46 at its forward end. This latch, seen in FIGS. 2, 4 and comprises a rearwardly directed blade 47 and a forwardly directed lever 48 which may be pressed by an actuating rod 49 in order to tilt up the latch blade. The gaps at 50 in the latch blade permit passage of the mount heads 28, as will become apparent subsequently. When the lamp plates are loaded on the grid, the latch blade is inserted between them that is between the rims of the faceplate and backplate along the front side of the lamp. The front dolly is now run forward into the lehring section of the oven and the lamp plates here attain a temperature in the range of 550 to 650 C., desirably approximately 600 C. During this time, lehring of the phosphor coating is accomplished and the latch blade between the two plates assures enough separation that the gases resulting from the decomposition of the organic phosphor binder escape readily.

While the lamp plates are in the lehring section of the oven, a pair of spaced gas burners 51 are caused momentarily to play hard sharp flames near the corners of the margin on the rear edge of the lamp plates. The purpose of this operation is to cause a viscous fusion of the margins at two spaced points 9a. These fusions are then used as a hinge to maintain the lamp plates in alignment when the front edge is subsequently lifted up for electrode insertion. It will be apparent that with more refined apparatus for maintaining the lamp plates in alignment, this step of tacking together the rear edges of the plates could be eliminated.

Mount pin and electrode insertion The front dolly now moves forward into the sealing section of the oven and carries the lamp plates and the grid-die 43 directly over the square platen 52 of a high pressure hydraulic press. However the platen at this time remains below and clear of the dolly as indicated in FIG. 4. Actuating rod 49 now moves down and causes the latch blade to lift up the front edge of the backplate as indicated at 3:1. The previously mentioned tack points indicated at 9a at the rear edge now serve as viscous hinges.

Mount heads 28, each loaded with an electrode bridge structure 10, now move forward through the apertures 8 27 in the furnace wall to position the electrodes between the lamp plates at the ends of the outer channelways. Each mount head comprises a tapered mount pin 53 with a flat lower surface; the mount pins may otherwise be described as longitudinally split cones. On each side of the mount pin there is provided a hollow pin 54 in which the outermost section 0 of the electrode inleads are inserted. The mount heads are supported at the forward ends of slidable rods 55 which are actuated through a crosshead 56 by means of a hydraulic cylinder 57 (FIG. 2). The mount heads position the electrodes such that the dumet sections b of the inleads overlie the lamp plate margins. Where a backplate notched out at 16, 17 is used, the dumet sections will be placed in line with the notches. Actuating rod 49 is now moved up to release the hinge latch and allow the backplate to drop back in place.

Press sealing 'Platen 52 on piston 59 of the hydraulic press now rises up through the tines of dolly 31 and lifts grid 43 just clear of the dolly. Another portion of the press (not shown in the drawing) engages the supporting structure for the mount heads through drive rod 59. The supporting structure may slide up and down on vertical rod 60 and thenceforth is carried upward along with the grid 43 through any further upward movement of the platen of the hydraulic press. Front dolly 31 is now moved forward sufficiently to clear latch blade 47 from between the margins of the lamp plates. Dolly 31 is now left as shown in FIG. 5 until the processing of this lamp is completed.

Press platen 52 now carries the lamp plates, supported on grid 43 which henceforth serves as a die, upward into engagement with stationary mold 61. Mold 61 is held immobile by a massive superstructure (not shown in the drawing) commensurate in strength to the thrust of the hydraulic cylinder. The hydraulic cylinder used is capable of providing a 100,000 pound thrust.

Mold 61 is in the form of a hollow square and only its rim 62 contacts the margin of the backplate. The front side of the mold is notched out with semicircular tapered openings 62 directly over the mount pins 53 in order to give relief and form semicircular tapered exhaust passageways or ports through the lamp rim or ledge seal, as indicated at 530 in FIG. 10a.

The dependent square rim 62 of the mold 61 is the operative part of the mold which engages the upper surface of the glass plate margin. The lower surface of the glass plate margin is engaged by the outer members of grid 43 which now forms a cooperating die. In general, the mold surface and the die surface are both flat, exception made of course for the semicircular apertures 63 in the front side of the mold for forming the exhaust passageways. However, if it is desired to provide any special forms in the marginal ledge of the lamp, a suitable insert or boss or notch may be provided in either the mold or die surface. For instance matching protuberances or bosses may be provided in the front side of the die in order to form the forward notches 20 which are useful for attaching base terminal structures to the marginal ledge of the lamp.

For sealing the lime glass lamp plates 1 have found a temperature in the range of 600 to 700 C., (preferably about 650 C. to be desirable. Glass will generally crack and fracture if struck a sharp blow in this temperature range. The ledge seal which is formed is about /8" wide and has a total peripheral length of about 46". The pressure applied over the sealing area is in the range of 2,000 to 4,000 pounds per square inch, preferably approximately 3,000 pounds per square inch. It takes from 1 to 15 seconds to complete the seal depending upon conditions. At 650 C. and 3000 lbs. pressure, approximately 3 seconds are a suitable time. Shorter times are possible if higher pressures or higher temperatures are utilized, and vice versa.

plates against the mold.

Just prior to the engagement of the lamp by the upper mold, it engages a secondary center press 64. The center press is in the form of a grid of parallel dependent bars 65 and may be drawn up and recessed in the square cavity of mold 61. The center press or grid structure is powered by a medium pressure cylinder (not illustrated) located above the top wall of the oven, through the intermediary of a pair of drive rods 66 which pass through apertures in the mold 61 and also through the top wall of the oven. The bars 65 of the center press are disposed so as to contact the glass of the backplate at the partitions 7 between channelways and they are in line with the internal bars 44 of die 43 which underlie the valleys in the faceplate. Desirably the center press is moved down and engages the lamp prior to the engagement of the lamp margins by the die 61. The center press engages the glass at the partitions 7 with relatively low pressure, for instance about 250 pounds per square inch. The term low is of course used in a comparative sense with respect to the high pressure, for instance 3000 pounds per square inch, with which the margin of the lamp is engaged. The center press serves to seat positively the flat areas or partitions in the backplate against the mating flat areas in the faceplate and also prevents warpage of the plates during the sealing of the margin. The glass of the two plates is not sealed together at the partitions, and desirably phosphor is imprisoned between the glass surfaces thereat. The presence of phosphor in these areas is desirable primarily from an appearance standpoint, but it is also useful to prevent a seal from being made or to prevent the glass surfaces from sticking together.

After it has engaged the lamp, the center press moves up with the lamp into the cavity within mold 61, meanwhile exerting a substantially constant pressure. The main high pressure hydraulic press continues the upward movement of platen 52 to press the margin of the glass Initially low pressure is ap plied and the mount heads and pins are withdrawn. Then high pressure is applied. After the seal is made, the platen is lowered but the center press is maintained in engagement with the lamp and follows it down, meanwhile exerting constant pressure on the partitions. The mount heads are then withdrawn out of the oven, the lamp is now sealed and ready for exhaust and electrode activation.

Marginal ledge seal structure The ledge seal structure which is obtained by the preceding low temperature very high pressure sealing method is decidedly different from what would be obtained in a comparable structure by ordinary flame or electric sealing. With these other sealing methods, the tendency is to obtain fusion of the glass at the very outermost edge of the sealing margins. This leaves a long narrow crack between the two glass surfaces of the margins. Such a crack may collect contaminants including organic phosphor-binder and gaseous impurities, and is exceedingly diflicult to outgas. In the absence of successful outgassing, the lamp will of course become contaminated during subsequent use and the presence of impurities may cause hard starting or present other difliculties.

Also, with electric resistance welding particularly, the long narrow ledges of glass which form the margin, being sealed at the very outermost edge only, may exert a large bending moment at the seal when temperature gradients occur and the result is an inherently weak vitreous structure.

By my sealing method, a wide sealed or fused margin is obtained which may be described as a ledge seal. Even though the glass is not at all soft in the ordinary sense at the sealing temperature, the tremendous pressure on it causes it to flow outwardly in both directions under the die and mold surfaces. The initial condition of the marginal ledge prior to scaling is shown in cross-section at 9 in FIG. 9a, and after sealing at 9b in FIG. 9b. The glass has been squeezed left and right as indicated by arrow 67, and the thickness of the ledge seal is less than the sum of the original margin thicknesses, for instance 15% less. The flow of the glass forms at the outer edge a new surface 90, and at the inner edge within the lamp a curved fillet 9d. The size or thickness of the fillet 9d has been exaggerated in the drawing. In actual practice it may be but a few thousandths of an inch in thickness (height) but is unmistakably present and can readily be seen with a low-power microscope. The important factor as regards the fillet is that the two glass surfaces of the backplate and faceplate do not merely come together along curving tangents but actually meet at a finite well defined line with a reversal in curvature of the glass sur face. This results in a strong vitreous structure. In a panel lamp, it is particularly important that the marginal ledge be strong because it is the part of the lamp which is most likely to be struck and abused. Another advantage of the illustrated seal structure is that the internal gap at 9d is fairly open and therefore can be outgassed readily during subsequent lamp processing.

The glass of the two plates is not sealed or fused together under the partitions 7. As may be seen in FIG. 9b, the flat glass portions at 7 are merely pressed together and the faceplate phosphor is desirably continued in these areas and imprisoned between the glass surfaces as indicated at 18.

Exhaust, gas fill, and electrode activation The mount heads 28 (previously withdrawn) along with the slide rods 55 which support them and their actuating mechanism are now lifted up and clear up the furnace apertures 27 by riding up on vertical rods 59. The exhaust head carriage 68 is now advanced on slide rods 69 by hydraulic cylinder 70 and the exhaust heads 29 are moved forward through the apertures 27 in the furnace wall and into engagement with the ledge-sealed lamp. The lamp is cooled to 450-550 C., desirably about 500 C.

The two metal exhaust tubes 71 are generally cylindrical but with the underside flat. The nose 72 is tapered at a relatively blunt angle, approximately 45, and the upper portion is conical for about 270 of arc and flat on the underside. The shape of the nose can be seen in FIG. 10a and also in FIG. 12 by the imprint which it leaves on the end of the vitreous exhaust passageway or port. The flat conical upper portion is seen at 72a and the straight sloping lower portion at 72b. The exhaust tube is heated to a temperature somewhat higher than that of the lamp by means of a small gas burner 73 supplied with gas by tube 74. It directs a flame on the exhaust tube and can be moved back and forth longitudinally. Desirably the tip of the exhaust tube is heated sufiiciently that it softens the glass slightly on immediate contact. It is pressed with substantial force against the glass of the exhaust port of the lamp. The lamp of course is meanwhile held in place by the pressure exerted thereon by the center press 64. The heat of the exhaust tube tips and the force with which they are pressed in causes a slight deformation or plastic flow of the glass at the exhaust apertures, causing it to conform to the nose or tip configuration of the exhaust tubes, hermetic seals being thereby obtained. During exhaust, the exhaust tubes are maintained approximately at lamp temperature.

The lamp is now evacuated through the exhaust tube and provided with a filling of mercury vapor. The electrode inleads 12, 13 are contacted by suitable means and a momentary flow of current passed through the electrodes to begin the activation. The lamp is then again exhausted in order to remove the carbon dioxide and other contaminants evolved during activation of the electrodes wherein the alkaline earth carbonate coatings on the electrodes are converted'to oxide. Another charge of mercury vapor is then introduced, current again momentarily flowed through the electrodes at a slightly higher intensity, and the contaminants again exhausted. This cycle may be repeated several times with gradually increasing intensity of current until the electrodes are completely activated and the lamp thoroughly outgassed. A measured charge of mercury is then introduced along with an inert filling gas such as argon and the lamp is now ready to be tipped-off.

To tip-off the lamp, the exhaust passageways 53a are collapsed into the rim or marginal ledge seal of the lamps. This may be done, as indicated in FIG. 7b, by moving burner 73 forward and playing a hard sharp flame against the glass of the exhaust passageway 53b immediately ahead of the nose of the exhaust tube. Since the internal pressure within the lamp is now very low, atmospheric pressure causes the softened glass to collapse and this seals the exhaust passageway. However I have found it desirable to assist this process by pressing a heated metal bar 75 which may be described as a dull rounded blade into the glass. The blade is carried at the forward end of a hinged lever 76 which is tipped-down to bring the blade into engagement with the glass as shown in FIG. 7c. The tipping-bar causes a generally wedgeshaped depression or notch to be formed in the glass of the marginal ledge transverse to the exhaust passageway and with the general appearance indicated at 75a in FIG. 13.

The lamp is now tipped-off, that is completely sealed off from the atmosphere and the exhaust heads are Withdrawn. The upstanding lip 72a which remains may be left as is. Alternatively, if its appearance is objectionable or if it interferes with the placement of a base on the marginal ledge at this point, it may be collapsed down by playing a hard sharp flame thereon, assisted by mechanical pressing means if desired.

Unloading and annealing The center press 64 is now raised to release the lamp and the lamp is lifted off the grid die 43 by bar elevators 77 supported on vertical rods 78 which rise through passageways in the platen 52. The reardolly 32 which has previously been entered into the oven in order to bring it up to oven temperature, is now run in under the lamp as indicated in FIG. 8. The lamp, now supported on the fork tines of dolly 32, is run back into the lehring section of the oven and stopped with the lamp directly over bar elevators 79. A rectangular sheet metal can 81 is supported on side dolly 33 in the lateral section of the oven. A cover 82 fits over the can and may be raised off the can by means of bar elevators 83 which engage a pair of transverse bars 84 fastened to the cover. The cover is raised off the can, and the can on side dolly 33 is now run in under the lamp and immediately above bar elevators 79. Bar elevators 79 rise up through suitable apertures in the bottom wall of the can, lift the lamp off rear dolly 32 which is then backed out of the oven and out of the way, and the elevators 79 then lower the lamp into the can. The lamp seats in the can by engagement of the marginal ledge seal 9 of the lamp with a marginal ledge 85 within the can. The side dolly is then run back under the cover 82, the cover lowered onto the can, and the dolly then run out through the exit door 25. The lamp is then slowly annealed or tempered within the can by placing it, can and all, in a cooling oven after which the lamp may be based in any desired fashion.

Conclusion My invention thus provides a radically new method for making electric discharge lamps and at the same time provides a lamp having structural features quite different from what has existed heretofore. My process has been described in connection with a specific configuration of fluorescent panel lamp; this is to be taken as illustrative only of the principles involved. The 10w temperature high pressure rim sealing process of my invention can obviously be applied to the manufacture of other sealed devices than a fluorescent panel lamp and is generally useful in the manufacture of sealed electrical devices including, by Way of example and not by way of limitation, electron discharge devices and incandescent lamps. My method of sealing electrode inleads through a marginal rim or ledge seal, and also my method of forming an exhaust passageway or port through such a ledge seal, can be used wherever the appropriate glass or vitreous configuration exists, irrespectively of the final use to which it is to be put. Likewise the related method of evacuating a sealed vitreous structure by means of such an exhaust passageway through engagement with the rim of a heated exhaust tube under substantial pressure may be used for the evacuation of sealed glass or vitreous devices generally. The unique vitreous structures which are obtained through the application of these methods, such as for example a wide ledge seal with an internal fillet, or a vitreous exhaust passageway tipped-oif by wall collapse with a transversely pressed blade notch, are of general utility and not limited to the specific application in connection with which they have been described.

The scope of the invention is therefore to be determined by the appended claims which are intended to cover the various aspects of the invention and such modifications thereof as fall within its true spirit and scope.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A sealed evacuated electric device comprising a vitreous envelope formed of a pair of vitreous plates defining an enclosure and fused together along their overlapping margins to provide a vitreous ledge seal, and an exhaust passageway formed in said ledge seal between said overlapping margins and tipped-off by a collapse of the walls thereof into said ledge.

2. A sealed evacuated electric device comprising a vitreous envelope formed of a pair of glass plates defining an enclosure and fused together along their overlapping margins to provide a vitreous ledge seal, and an exhaust passageway formed in said ledge seal between said overlapping margins and tipped-off by a blade-shaped notch in said ledge transverse to said passageway collapsing one of said margins into the other.

3. A sealed evacuated electric device comprising a vitreous envelope formed of a pair of vitreous plates defining an enclosure and fused together along their overlapping margins to provide a vitreous ledge seal, a pair of inlead conductors sealed through said ledge seal between said overlapping margins, and an exhaust passageway formed in said ledge seal between said overlapping margins and tipped-off by a collapse of the walls thereof into said ledge seal.

References Cited by the Examiner UNITED STATES PATENTS 2,220,741 11/1940 Thorson 17450.52 2,269,165 1/1942 Kling 174-50.52 2,406,146 8/1946 Holmes 313204 2,555,749 6/1951 Krefit 313204 X 2,620,598 12/1952 Jobling-Purser et a1. 49-82 2,677,920 5/1954 Danzin et al 4982 2,874,710 2/1959 Boehme 137--1 2,965,114 12/1960 Harden 137-1 2,987,640 6/1961 Paolino 313-204 3,047,763 7/1962 Inman 3 l3-109 FOREIGN PATENTS 94,978 8/1960 Netherlands.

GEORGE N. WESTBY, Primary Examiner. JOHN P. WIL'DMAN, E. JAMES SAX, Examiners. 

1. A SEALED EVACUATED ELECTRIC DEVICE COMPRISING A VITREOUS ENVELOPE FORMED OF A PAIR OF VITREOUS PLATES DEFINING AN ENCLOSURE AND FUSED TOGETHER ALONG THEIR OVERLAPPING MARGINS TO PROVIDE A VITREOUS LEDGE SEAL, AND AN EXHAUST 